Problem: $ A = \left[\begin{array}{rrr}1 & 2 & 1 \\ 2 & 0 & 2 \\ 1 & 1 & 2\end{array}\right]$ What is $ A^{-1}$ ?
$ = \left[\begin{array}{rrr}\frac{1}{2} & \frac{3}{4} & -1 \\ \frac{1}{2} & -\frac{1}{4} & 0 \\ -\frac{1}{2} & -\frac{1}{4} & 1\end{array}\right]$